Scientific Measurement CHAPTER 3 Scientific Measurement

Scientific Measurement International system of Units (SI) Revised version of the metric system Grams and liters not pounds and ounces Base units length, mass, temp, time, etc. Derived units can be calculated density, volume, pressure

Two Types of Measurements Qualitative = descriptive and non-numerical EX: color, odor, texture, etc Quantitative = definite form, numbers and units EX: temperature, mass, length, volume, density

Scientific notation Used to write very big and very small numbers 6.02 X 1023 instead of 602000000000000000000000 Number is written as the product of 2 numbers: a coefficient and Exponent N X 10x N is a coefficient; a number that is between 1 and ten X is an exponent (integer)

Scientific Notation rules Coefficient: expressed as a number between 1 and 10 (not including 10) Exponents if the # is greater than ten, the exponent is positive if the # is less than one, the exponent is negative A number between 1 and ten will not be converted

Converting a number into scientific notation . 2 500 000 000 9 8 7 6 5 4 3 2 1 Step #1: Insert an understood decimal point Step #2: Decide where the decimal must end up so that one number is to its left Step #3: Count how many places you bounce the decimal point The exponent is the number of places we moved the decimal. Step #4: Re-write in the form M x 10n 2.5 X 109

Converting a number into scientific notation 2 500 000 000 2.5 X 109 The exponent is positive because the number we started with was greater than 10.

Converting a number into scientific notation 1 2 3 4 5 Step #1 Locate the decimal Step #2 Decide where the decimal must end up so that one number is to its left Step #3 count how many places you bounce the decimal point Step #4 Re-write in the form N x 10x

Converting a number into scientific notation The exponent is negative because the number we started with was less than 1.

CHEM-practice… Convert the following 45000 written as 510 written as 602000 written as 4.5 x 10 -4 written as 3.2 x 10 -2 written as 2.89 x 10 -3 written as 4.5 x 10 4 5.3 x 10 2 6.02 x 10 5 0.00045 0.032 0.00289 If you moved the decimal point to the left, your exponent is positive If you moved to the right, your exponent is negative

Uncertainty in measurement Accuracy = how close a measurement comes to the actual or true value of whatever is measured Precision = how close a series of measurements are to one another Precise, not accurate

Uncertainty in measurement Accurate, not precise

Uncertainty in measurement Not precise, not accurate

Uncertainty in measurement Precise AND accurate

Error in measurement Accepted/actual value Experimental value the correct value based on reliable references Experimental value the value measured in the lab Error = accepted – experimental % error = I accepted – experimental I x 100 accepted

Calculating Error A recipe says you should make 36 cookies but you only got 33 cookies. What is your percent error? Percent Error = I accepted – experimental I x 100 accepted accepted = 36 experimental = 33 Percent Error = I 36-33 I x 100 36 = 8.3 % error

Significant figures Numbers that include ALL digits that can be known plus a last digit that is estimated Digits that have meaning

Significant figures Rules regarding zeros Every non-zero digit is significant (567) Zeros between non-zeros are sig (305) Zeros in front of nonzeros are placeholders… NOT SIG (0.00035) Zeros following a nonzero only sig if The come after a decimal point (3.4210) Or a decimal follows (3420.) 3420

Significant figures HOW MANY SIG FIGS?????? 4.21 4.210 0.0421 42.10 42010 42010.0 (3) (4) (3) (4) (4) (6)

Rounding SIG FIGS If the digit after the last sig fig is less than 5, drop all digits after the last sig fig (4 or below, let it go) If the digit after the last sig fig is 5 or greater, round the value of the digit in the last sig place up by 1 (5 and above, give it a shove) 1 Sig FIG 5 4.8610 2Sig FIG 4.9 3 Sig FIG 4.86

Rounding SIG FIGS Round each of the following numbers to 2 SIG FIGS 4.21 4.210 0.0421 42.10 4210 42010 42010.0 4.2 0.042 42 4200 42000

Scientific Measurement International system of Units (SI) Revised version of the metric system Grams and liters not pounds and ounces Base units length, mass, temp, time, etc. Derived units can be calculated density, volume, pressure

DENSITY The ratio of an object’s mass to its volume Objects with the same volumes but different masses will have different densities The size, mass and arrangement of atoms affects a materials density Copper atoms are smaller than aluminum atoms. More copper atoms can fit in the cube. Copper atoms are also heavier than aluminum atoms. The combination of more and heavier atoms makes copper more dense than aluminum.

Calculating the Density of Water How can you go about determining the density of water? What kind of data do you need to measure? Does a small amount of water have the same density as a large amount of water? Do you think hot water and cold water have the same density?

Calculating Density Equation: Density = mass ÷ volume Units: g/cm3 or g/ml

Calculating Density A copper penny has a mass of 3.1 g and a volume of 0.35 cm3. What is the density of copper? Equation: D = m/V Units: g/cm3

Using Density to identify an unknown A student finds a shiny piece of metal that she thinks is aluminum. In the lab, she determines that the metal has a volume of 245 cm3 and a mass of 612 g. Calculate the density. Is it aluminum? Density Al= 2.70 g/cm3 Equation: D = m/V Units: g/cm3

Temperature Defined: direction of heat transfer When two objects are in contact, heat moves from the object at the higher temperature to the object at the lower temperature

Temperature scales Celsius Kelvin scale Uses two determined temperatures as reference temp Boiling point of water = 100oC Freezing point of water = 0 oC Kelvin scale Boiling point of water = 373 K Freezing point of water = 273 K Notice no degree sign 0 K = absolute zero or the point at which all motion stops

Converting between Celsius and kelvin K = oC + 273 Ex: convert 25 oC to K K = 25 oC + 273 K = 298K oC = K - 273 Ex: convert 0K to oC oC = 0K - 273 oC = -273 oC